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Stock-Based Compensation - Summary of Weighted Average Assumptions in Fair Value of Option Grant (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Employee Stock Option [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Estimated grant date fair value per share $ 2.83 $ 2.14 $ 1.95
Expected life (years) 4 years 5 months 16 days 4 years 6 months 4 days 4 years 3 months 18 days
Risk-free interest rate 0.72% 1.83% 1.91%
Volatility 47.00% 47.00% 51.00%
Employee Stock Purchase Plan [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Estimated grant date fair value per share $ 1.94 $ 1.81 $ 1.49
Expected life (years) 9 months 18 days 9 months 18 days 9 months 18 days
Risk-free interest rate 0.20% 0.10% 0.20%
Volatility 43.00% 45.00% 36.00%